Grasping cap on gas piping (6)
I believe the answer is:
greedy
'grasping' is the definition.
(synonyms)
'cap on gas piping' is the wordplay.
'cap on' suggests taking the first letters (I've seen 'caps on' mean this (the top letters or 'caps')).
'piping' becomes 'reedy' (both can mean thin or high-pitched).
The initial letter of 'gas' is 'g'.
'g'+'reedy'='GREEDY'
(Other definitions for greedy that I've seen before include "Overeating" , "Having excessive desire for food or money" , "Avaricious and acquisitive" , "Covetous, avaricious" , "Having a voracious appetite" .)